Laboratory and field evaluation of Bacillus thuringiensis and B. sphaericus against mosquito larvae

Laboratory and field trials were carried out with two formulations of Bacillus thuringiensis and four strains of Bacillus sphaericus (B 42, B 64, B 87 and B 33) against mosquito larvae in different breeding habitats of Tezpur, Assam. LC90 of B. thuringiensis var israelensis (formulation Teknar) against Ae. albopictus, Cx. quinquefasciatus and Cx. gelidus were recorded as 0.443, 0.453 and 2.15 ppm respectively and LC90 of B. thuringiensis (Deltox: VCRC B-17) against Ae. albopictus, Cx. quinquefasciatus, Cx. gelidus and Cx. malayi were 8.414, 11.22, 5.24 and 6.761 ppm respectively. LC90 of B. sphaericus strains B 42, B 64, B 87 and B 33 against Cx. quinquefasciatus were 0.055, 0.115, 0.046 and 0.257 ppm respectively. At the dosage of 1 l/ha 87 per cent mortality was achieved after 24 hrs with Bti and it increased to 90-95 per cent at 1.5 l/ha. In polluted cemented drains 93-97 per cent kill of Cx. quinquefasciatus was observed at 2.5 l/ha. Out of four strains of B. sphaericus evaluated, strain B 87 was found to be the most effective as 87-96 per cent kill was achieved with only 0.1 kg/ha for Cx. quinquefasciatus, Cx. vishnui and A. vagus. For others 0.2 kg/ha dosage, eliminated 96-100 per cent Cx. vishnui gr. for B 42, 92-93 per cent for B 64 and 90-93 per cent for B 33 strain.